Group VIII metals, such as platinum or palladium, have been used extensively as catalysts. One such use has been as a catalyst for the reaction of hydrogen and oxygen to form hydrogen peroxide.
U.S. Pat. No. 5,480,629 uses Group VIII metals to catalyze the reaction of hydrogen and oxygen by forming pillars of alkyl bisphosphonic acid with dicationic bipyridinium (viologen) groups incorporated into the alkyl chain. These catalysts were prepared by first synthesizing a porous viologen-phosphonate material. The porous materials were either Zr or Hf complexes of .sup.2- O.sub.3 PCH.sub.2 CH.sub.2 viologen CH.sub.2 CH.sub.2 PO.sub.3.sup.2- (PV), prepared as either bulk materials or thin films grown on high surface area supports. The positive charge of the viologen group gives the lattice a net positive charge, which is compensated by halide ions, found in the pores of the solid. These halide ions can be readily exchanged for metal salts (e.g. MCl.sub.4.sup.2-, M=Pd, Pt), however, complete exchange requires several treatments of the solid with solutions of the metal salt. The final step in the preparation of the catalyst is the reduction of the metal salt to a colloidal metal particle. The goal is to trap the metal particles within the pores of the material, such that they can catalyze electron transfer from hydrogen to viologen. Direct reduction of viologen with hydrogen is not possible. The reduced form of viologen will then react very rapidly with oxygen to produce hydrogen peroxide. While the procedure outlined above does make effective catalyst materials, the materials are not ideal. The ion exchange process fails to fully incorporate metal ions, since the metal ions themselves blocks the pores from further exchange as the level of metal incorporation gets high. The second, and more significant problem, is that the ion exchange process leave a significant amount of metal and metal salt on the outside of the particles. We have observed this by electron microscopic studies. The metal on the outside of the particle can engage in deleterious side reactions that significantly decrease the amount of hydrogen peroxide that is formed. Supported metals (e.g. Pd or Pt) will efficiently decompose hydrogen peroxide. In order to achieve the highest levels of peroxide and more generally to keep the catalysis reactions confined to a single site (viologen groups) it is important to prepare materials with little or no metal on the outside of the catalyst particles and significant amounts of metal within the pores of the materials.